Important considerations in designing electrical power systems for unmanned aircraft systems

Pneumatic and hydraulic actuators and controls are fast becoming the dinosaurs of the unmanned aerial vehicle (UAV) world, replaced with electrical motors and electronic computers and sensors. This trend places an increasing burden on the team member who is tasked with the design of the unmanned electrical power distribution system. Five factors that affect the performance and reliability of the platform must be considered when specifying components for the UAV power system. Prioritizing each of these factors in your power distribution design is critical.

Jan 14th, 2014
UAS
UAS

By Ralph Livingstone, Chief Engineer, Abbott Technologies Inc.

Pneumatic and hydraulic actuators and controls are fast becoming the dinosaurs of the unmanned aerial vehicle (UAV) world, replaced with electrical motors and electronic computers and sensors. This trend places an increasing burden on the team member who is tasked with the design of the unmanned electrical power distribution system. Five factors that affect the performance and reliability of the platform must be considered when specifying components for the UAV power system. Prioritizing each of these factors in your power distribution design is critical.

1. Efficiency and Weight

The efficiency of power converters and bus switches will affect the use of the available fuel load and thermal management in the platform. This is true whether the unmanned uses MIL-STD-704 400 Hz AC power, a high-voltage DC bus, or a low-voltage DC bus. Ultimately, waste heat energy derived from fuel must be disposed of, but this can be highly problematic in a high-altitude UAV where avionics are often located in pressurized compartments and composite construction makes heat transfer extremely challenging.

Reduction of the system heat load will reduce the weight of the cooling system and extend the range and payload capacity of the UAV, thereby increasing overall efficiency. Therefore, liquid cooling using fuel or polyalphaolefins is sometimes employed in these vehicles.

Furthermore, designing power converters or transformer rectifier units that meet specific system requirements for minimum size and weight will result in more efficient use of fuel and available payload capacity. Advanced thermal design techniques, a lightweight case, potting and connector materials, and more recent semiconductor technologies such as SiC are typically used to achieve the appropriate balance between weight and efficiency.

2. Quality

As size and weight of power conversion or control equipment decreases, maintaining reliability becomes a growing concern. It becomes essential that an AS9100C certified manufacturer is chosen for the project, to ensure the manufacturing processes are being carefully controlled and monitored to maintain overall reliability. Also, the system designer must work closely with the component manufacturer, so all aspects of the design are carefully analyzed and components are selected to work reliably in the anticipated application of the system.

3. Built-in Test and Control Functions

Adding test, control, and monitoring functions to an existing system using COTS power converters could be costly and will undoubtedly waste space and weight. Therefore, the system designer must determine the needs for specific control and monitoring functions within the power system components as early in the design process as possible.

As UAV missions become more complex, the demand for accurate, real-time system information continues to increase. For example, you’ll need to test, control, and monitor power converters to include output voltage and current, temperature and input, as well as control factors like engagement or battle-short of protective features as well as the enable/disable sequencing of converters. The increasing demand for test, control, and monitoring functions will continue to grow in the future, so you must prioritize them early in your power system design process.

4. Flexibility

In order to save time and money in the future, work with a supplier that is both able and prepared to modify its standard product in a timely manner to meet all of your specific system requirements without excessive non-recurring charges. Flexibility is critical to the UAV design over the long-term. Designing a flexible power distribution system will not only help you to minimize fuel waste in the future, but it will enable the system to easily grow with your evolving mission requirements.

5. Cost of the Components

Choose reliable but flexible components so you don’t incur large expenses in the future when you need to modify your UAV power distribution system. Furthermore, design a system that maximizes efficiency so you can control costs while reducing fuel waste. A flexible and balanced system designed today with high-quality, military-grade components will save you money and reduce problems over the long term.

To learn more about choosing components for your UAV power system, contact Abbott Technologies at (818) 504-0644 or visit www.abbott-tech.com.

UAS images courtesy Shutterstock.

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